(1) Field of the Invention
The present invention relates to a roller pump for fluid transfer, such as blood circulation, dialytic fluid circulation or fluid medicine injection, and more particularly, to an improved roller pump with high rotational accuracy, compactness in size and excellent durability.
(2) Description of the Prior Art
In general, roller pumps are simply structured and generate constant flow, and employ disposable tubes as a member for fluid transfer; these advantages make them ideal for us as a fluid transfer devices for blood circulation circuits, dialytic fluid circulation circuits or injecting apparatuses for fluid medicines.
A conventional roller pump 10, as shown in FIG. 1, comprises a drive mechanism 14 furnished with a drive shaft 12, a rotating shaft 16 which rotates according to the rotation of drive shaft 12, and a hollow pump head 20 fixed to a housing 18 to which drive mechanism 14 is attached. This pump head 20 integrally incorporates a bearing block 24 through which rotating shaft 16 is inserted and rotatably supported by a pair of bearings 22 and a stator 26 arranged to the upper portion of bearing block 24. On the upper surface of stator 26 is formed a recess 28 through which the upper end of rotating shaft 16 is protruded. While this recess 28 is radially and outwardly spaced at a certain distance from the outer circumferential surface of rotating shaft 16, its inner circumferential surface 28a is coaxial with rotating shaft 16.
Rotor 30 is attached to the upper portion of rotating shaft 16 in such a way as to be placed inside recess 28 of stator 26 and to stay opposite the inner circumferential surface 28a thereof. This rotor 30 is fixed to rotating shaft 16 through a bolt 32, and is so constructed as to integrally rotate along with rotating shaft 16. On the outer circumferential surface of rotor 30, at least one roller 34 is arranged so as to rotate around its own axes. A tube 36 which is filled with blood or other fluid materials is placed between rotor 30 and stator 26. Tube 36 is clamped between respective rollers 34, which are attached to rotor 30, and inner circumferential surface 28a of stator 26, thereby maintaining tube 36 in a closed state at the point at which it is clamped.
Thus, in a conventional roller pump 10, rotor 30 is rotated by the rotational motion of rotating shaft 16 driven by drive mechanism 14, and the clamped portions of tube 36 move according to the revolution of rollers 34 around rotating shaft 16. Therefore, fluid inside tube 36 is transferred according to the revolution of rollers 34. It is to be noted that by the revolution of roller 34, tube 36 comes off easily after being clamped between rollers 34 and inner circumferential surface 28a ; in order to prevent this, tube guides 38 are provided which hold tube 36 in position.
In these roller pumps of conventional construction, rotor 30 is attached to rotating shaft 16 by an open-sided supporting structure. Therefore, when rollers 34 close tube 36, a reaction force perpendicular to the axis of rotating shaft 16 occurs. Rotating shaft 16 is thereby bent by this force, and when rotated in this state, swing tends to occur.
Under these conditions, if rotating shaft 16 swings, the clearance between each roller 34 and inner circumferential surface 28a varies, thus causing unevenness in the closed state of tube 36. This causes the stable transfer of the fluid to deteriorate, and durability of roller pump 10 is shortened.
Consequently, the following two measures to prevent the swing of rotating shaft 16 are considered:
(1) rotor 30 is attached to rotating shaft 16 by a both-sided supporting structure; PA0 (2) while keeping an open-sided supporting structure, the shaft diameter is increased, and large-bore bearings of high durability are employed in order to increase the rigidity of rotating shaft 16.
Considering the measures mentioned above; in measure (1), the construction of the pump becomes complicated, and furthermore attaching and detaching the tube to the clearance between rotor 30 and stator 26 becomes difficult, which is far from practical to use. This eventually leads us to choose measure (2).
In measure (2) as mentioned above, however, although the swing of rotating shaft 16 is prevented, the shaft diameter of rotating shaft 16 becomes large and the bore of the bearing is also increased, resulting in a total increase in both the size and the weight of the roller pump.